Samples handled in laboratories may be in many types of vessels, according to need. For example, the diameters of the vessels vary from a few millimeters to a few centimeters. In general, larger entities, i.e. plates, are formed of the vessels. The plates also come in many sizes and shapes. The most commonly used plate is the so-called microtiter plate having 8.times.12 wells.
For the rationalization of assays it would be preferable if as many different types of plates as possible could be used in one and the same apparatus. In general, plates according to only a certain standard can be used in present-day apparatuses, such as optical analysers.
In certain optical analysers the sample-holding plate is handled in a holder in which the plate can be shifted over fractions of a millimeter in one given direction (e.g. iEMS Reader/Dispenser, Labsystems Oy, Finland). Thus it is possible to take into account small deviations from the standard of the outer dimension of the plate in the direction concerned. These apparatuses have in one edge of the plate holder adjustable stop screws, a movable wall, or a spring pressing against the plate.